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Abstract:

This disclosure provides a wideband antenna including a feed line, a
ground conductor plate and a radiating conductor element connected to the
feed line and facing the ground conductor plate at a distance from the
ground conductor plate. A parasitic conductor element is provided on a
side opposite to the ground conductor plate as viewed from the radiating
conductor plate and is insulated from these plates. A coupling adjusting
conductor plate is positioned between the radiating conductor element and
the parasitic conductor element, is configured to adjust an amount of
coupling between them, overlaps an area where the radiating conductor
element and the parasitic conductor element overlap, and straddles the
radiating conductor element in a direction orthogonal to the direction of
a current I that flows therein. Both end sides of the coupling adjusting
conductor plate are electrically connected to the ground conductor plate
via via-holes.

Claims:

1. A wideband antenna comprising: a ground conductor plate configured to
be connected to a ground potential; a radiating conductor element facing
the ground conductor plate at a distance from the ground conductor plate
and connected to a feed line; a parasitic conductor element on a side
opposite to the ground conductor plate as viewed from the radiating
conductor element, and insulated from the ground conductor plate and the
radiating conductor element; and a coupling adjusting conductor plate
positioned between the parasitic conductor element and the radiating
conductor element, and configured to adjust an amount of coupling between
the parasitic conductor element and the radiating conductor element,
wherein the coupling adjusting conductor plate partially overlaps an area
where the parasitic conductor element and the radiating conductor element
overlap each other, and straddles the radiating conductor element in a
direction orthogonal to a direction of a current that flows in the
radiating conductor element, the coupling adjusting conductor plate being
electrically connected at both end sides to the ground conductor plate.

2. The wideband antenna according to claim 1, wherein the both end sides
of the coupling adjusting conductor plate are connected to the ground
conductor plate by using a columnar conductor.

3. The wideband antenna according to claim 1, wherein: the feed line
includes a strip line, the strip line having: another ground conductor
plate that is provided on a side opposite to the radiating conductor
element as viewed from the ground conductor plate, and a strip conductor
that is provided between the other ground conductor plate and the ground
conductor plate and connecting to the radiating conductor element via a
connecting aperture provided in the ground conductor plate.

4. The wideband antenna according to claim 1, wherein: the feed line
includes a microstrip line, the microstrip line having a strip conductor
that is provided on a side opposite to the radiating conductor element as
viewed from the ground conductor plate, and the strip conductor of the
microstrip line connects to the radiating conductor element via a
connecting aperture provided in the ground conductor plate.

5. The wideband antenna according to claim 1, wherein the parasitic
conductor element includes a substantially rectangular conductor plate
that is cut off at a corner portion.

6. The wideband antenna according to claim 1, wherein the ground
conductor plate, the radiating conductor element, the parasitic conductor
element, and the coupling adjusting conductor plate are provided to a
multilayer substrate having a plurality of laminated insulating layers,
and are placed at positions different from each other with respect to a
thickness direction of the multilayer substrate.

7. The wideband antenna according to claim 1, wherein a width of the
coupling adjusting conductor plate in the orthogonal direction is greater
than a width of the radiating conductor element in the orthogonal
direction.

8. The wideband antenna according to claim 1, wherein a length of the
coupling adjusting conductor plate in the direction of the current is
less than the length of the of the radiating conductor element in the
direction of the current.

9. The wideband antenna according to claim 8, wherein the length of the
coupling adjusting conductor plate is about half the value of the length
of the radiating conductor element.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to International
Application No. PCT/JP2010/069537 filed on Nov. 3, 2010, and to Japanese
Patent Application No. 2010-015562 filed on Jan. 27, 2010, the entire
contents of each of these applications being incorporated herein by
reference in their entirety.

TECHNICAL FIELD

[0002] The technical field relates to a wideband antenna suitably used for
high frequency signals such as microwave and millimeter wave signals, for
example.

BACKGROUND

[0003] As an example of wideband antenna according to the related art, a
microstrip antenna (patch antenna) is known in which a radiating
conductor element and a ground conductor plate are provided facing each
other across a dielectric that is thin relative to the wavelength, and a
parasitic conductor element is provided on the radiating surface side of
the radiating conductor element. See, for example, Japanese Unexamined
Patent Application Publication No. 55-93305 (Patent Document 1). The
wideband antenna according to Patent Document 1 achieves bandwidth
enhancement by exploiting electromagnetic coupling between the radiating
conductor element and the parasitic conductor element.

[0004] Also, as another example of the related art, a configuration is
known in which, in addition to the configuration according to Patent
Document 1 mentioned above, two conductor plates that face each other
with a gap are placed between the radiating conductor element and the
parasitic conductor element, and these conductor plates are electrically
connected to the ground conductor plate. See, for example, Japanese
Unexamined Utility Model Registration Application Publication No. 4-27609
(Patent Document 2). In the wideband antenna according to Patent Document
2, the conductor plates are placed between the radiating conductor
element and the parasitic conductor element. This makes the
electromagnetic coupling between the radiating conductor element and the
parasitic conductor element stronger, which can lead to increased
bandwidth.

SUMMARY

[0005] The present disclosure provides a wideband antenna that can achieve
increased bandwidth while minimizing variations in characteristics.

[0006] According to one aspect of the disclosure, a wideband antenna
includes a ground conductor plate configured to be connected to a ground
potential, a radiating conductor element facing the ground conductor
plate at a distance from the ground conductor plate and connected to a
feed line, and a parasitic conductor element on a side opposite to the
ground conductor plate as viewed from the radiating conductor element and
insulated from the ground conductor plate and the radiating conductor
element. A coupling adjusting conductor plate is positioned between the
parasitic conductor element and the radiating conductor element, and is
configured to adjust an amount of coupling between the parasitic
conductor element and the radiating conductor element. The coupling
adjusting conductor plate partially overlaps an area where the parasitic
conductor element and the radiating conductor element overlap each other,
and straddles the radiating conductor element in a direction orthogonal
to a direction of a current that flows in the radiating conductor
element. The coupling adjusting conductor plate is electrically connected
at both end sides to the ground conductor plate.

[0007] According to a more specific embodiment, the both end sides of the
coupling adjusting conductor plate may be connected to the ground
conductor plate by using a columnar conductor.

[0008] In another more specific embodiment, the feed line may include a
strip line. The strip line may have another ground conductor plate that
is provided on a side opposite to the radiating conductor element as
viewed from the ground conductor plate, and a strip conductor that is
provided between the other ground conductor plate and the ground
conductor plate. The strip conductor of the strip line may connect to the
radiating conductor element via a connecting aperture that is provided in
the ground conductor plate.

[0009] In yet another more specific embodiment, the feed line may include
a microstrip line. The microstrip line may have a strip conductor that is
provided on a side opposite to the radiating conductor element as viewed
from the ground conductor plate. The strip conductor of the microstrip
line may connect to the radiating conductor element via a connecting
aperture that is provided in the ground conductor plate.

[0010] In another more specific embodiment according to the present
disclosure, the parasitic conductor element may include a substantially
rectangular conductor plate that is cut off at a corner portion.

[0011] In another more specific embodiment according to the present
disclosure, the ground conductor plate, the radiating conductor element,
the parasitic conductor element, and the coupling adjusting conductor
plate may be provided to a multilayer substrate having a plurality of
laminated insulating layers, and may be placed at positions different
from each other with respect to a thickness direction of the multilayer
substrate.

[0012] In still another more specific embodiment a width of the coupling
adjusting conductor plate in the orthogonal direction is greater than a
width of the radiating conductor element in the orthogonal direction.

[0013] In another more specific embodiment, a length of the coupling
adjusting conductor plate in the direction of the current is less than
the length of the of the radiating conductor element in the direction of
the current.

[0014] In another more specific embodiment, the length of the coupling
adjusting conductor plate is about half the value of the length of the
radiating conductor element.

BRIEF DESCRIPTION OF DRAWINGS

[0015]FIG. 1 is a perspective view illustrating a wideband patch antenna
according to a first exemplary embodiment.

[0016]FIG. 2 is a cross-sectional view of the wideband patch antenna
taken along the arrow II-II in FIG. 1.

[0017]FIG. 3 is a cross-sectional view of the wideband patch antenna
taken along the arrow III-III in FIG. 2.

[0018]FIG. 4 is a cross-sectional view of the wideband patch antenna
taken along the arrow IV-IV in FIG. 2.

[0019] FIG. 5 is an explanatory drawing illustrating the first resonant
mode of the wideband patch antenna at the same position as FIG. 2.

[0020]FIG. 6 is an explanatory drawing illustrating the second resonant
mode of the wideband patch antenna at the same position as FIG. 2.

[0021]FIG. 7 is a characteristic diagram illustrating the frequency
characteristics of return loss, for each of the first embodiment and a
first comparative example.

[0022]FIG. 8 is a characteristic diagram illustrating the frequency
characteristics of return loss, for each of the first embodiment and
second and third comparative examples.

[0023] FIG. 9 is a perspective view illustrating a wideband patch antenna
according to a second exemplary embodiment.

[0024] FIG. 10 is a cross-sectional view of the wideband patch antenna
taken along the arrow X-X in FIG. 9.

[0025] FIG. 11 is a cross-sectional view of the wideband patch antenna
taken along the arrow XI-XI in FIG. 10.

[0026]FIG. 12 is a cross-sectional view of the wideband patch antenna
taken along the arrow XII-XII in FIG. 10.

[0027]FIG. 13 is a perspective view illustrating a wideband patch antenna
according to a third exemplary embodiment.

[0028]FIG. 14 is a cross-sectional view of the wideband patch antenna
taken along the arrow XIV-XIV in FIG. 13.

[0029] FIG. 15 is a perspective view illustrating a wideband patch antenna
according to a fourth exemplary embodiment.

[0030]FIG. 16 is a cross-sectional view of the wideband patch antenna
according to the fourth embodiment taken at a position similar to FIG. 4.

[0031]FIG. 17 is a characteristic diagram illustrating the frequency
characteristics of return loss, for each of the fourth embodiment and a
fourth comparative example.

DETAILED DESCRIPTION

[0032] The inventors realized that in the wideband antenna according to
Patent Document 1, the dimension of the distance in the thickness
direction between the radiating conductor element and the parasitic
conductor element contributes greatly to the magnitude of electromagnetic
coupling, and hence there is a limit to bandwidth enhancement.

[0033] Additionally, in the wideband antenna according to Patent Document
2, owing to the structure of the conductor plates in which the conductor
plates are bent in an L-shape and their ends are attached to the ground
conductor plate by soldering, assembly of the conductor plates is
difficult, leading to low productivity. In addition, variations in
characteristics among individual antennas become significant.

[0034] The present disclosure provides a wideband antenna that can achieve
increased bandwidth while minimizing variations in characteristics.
Hereinafter, as an example of wideband antenna according to an exemplary
embodiment, a wideband patch antenna for use in the 60 GHz band is
described in detail with reference to the attached drawings.

[0035] FIGS. 1 to 4 illustrate a wideband patch antenna 1 according to a
first exemplary embodiment. The wideband patch antenna 1 includes a
multilayer substrate 2, a ground conductor plate 8, a radiating conductor
element 9, a parasitic conductor element 15, a coupling adjusting
conductor plate 16, and the like described later.

[0036] The multilayer substrate 2 is formed in a flat shape that extends
in parallel to, for example, the X-axis direction and the Y-axis
direction among the X-axis, Y-axis, and Z-axis directions that are
mutually orthogonal. The multilayer substrate 2 has a width dimension of
about several mm, for example, with respect to the Y-axis direction that
is the width direction, and has a length dimension of about several mm,
for example, with respect to the X-axis direction that is the length
direction. The multilayer substrate 2 also has a thickness dimension of
about several hundred μm, for example, with respect to the Z-axis
direction that is the thickness direction.

[0037] The multilayer substrate 2 can be formed by, for example, a low
temperature co-fired ceramic multilayer substrate (LTCC multilayer
substrate). The multilayer substrate 2 has five insulating layers 3 to 7
that are laminated in the Z-axis direction from its front side 2A toward
its back side 2B. The insulating layers 3 to 7 are each made of an
insulating ceramic material that can be fired at low temperatures of not
higher than 1000° C., and formed in a thin layer form.

[0038] The ground conductor plate 8 is formed by using, for example, a
conductive metallic material such as copper or silver, and is connected
to the ground. The ground conductor plate 8 is located between the
insulating layer 5 and the insulating layer 6, and covers substantially
the entire surface of the multilayer substrate 2. That is, the ground
conductor plate 8 covers substantially the entire upper surface of
insulating layer 6. The radiating conductor element 9 is provided on the
front side with respect to the ground conductor plate 8, and a strip line
10 is provided on the back side with respect to the ground conductor
plate 8. Accordingly, in order to provide connection between the
radiating conductor element 9 and the strip line 10, for example, a
substantially circular connecting aperture 8A is provided in the central
portion of the ground conductor plate 8.

[0039] The radiating conductor element 9 is formed in a substantially
rectangular shape by using a conductive metallic material similar to that
of the ground conductor plate 8, for example. The radiating conductor
element 9 faces the ground conductor plate 8 at a distance. Specifically,
the radiating conductor element 9 is placed between the insulating layer
5 and the insulating layer 4. The insulating layer 5 is placed between
the radiating conductor element 9 and the ground conductor plate 8.
Therefore, the radiating conductor element 9 faces the ground conductor
plate 8 while being insulated from the ground conductor plate 8.

[0040] As illustrated in FIG. 4, the radiating conductor element 9 has a
width dimension L1 of, for example, about several hundred μm in the
Y-axis direction, and has a length dimension L2 of, for example, about
several hundred μm in the X-axis direction. The length dimension L2 in
the X-axis direction of the radiating conductor element 9 is set to a
value that is one-half wavelength in electrical length of the high
frequency signal used, for example.

[0041] Further, a via-hole 14 described later is connected to the
radiating conductor element 9 at some point along the X-axis direction.
Also, the strip line 10 is connected to the radiating conductor element 9
via the via-hole 14. In the radiating conductor element 9, an electric
current I flows in the X-axis direction as electric power is fed from the
strip line 10 (see, FIG. 1).

[0042] As illustrated in FIGS. 1 to 4, the strip line 10 is provided on
the side opposite to the radiating conductor element 9 as viewed from the
ground conductor plate 8. The strip line 10 forms a feed line for feeding
electric power to the radiating conductor element 9. Specifically, the
strip line 10 includes another ground conductor plate 11 and a strip
conductor 12. The ground conductor plate 11 is provided on the side
opposite to the radiating conductor element 9 as viewed from the ground
conductor plate 8. The strip conductor 12 is provided between the ground
conductor plate 8 and the ground conductor plate 11. The ground conductor
plate 11 is provided on the back side 2B of the multilayer substrate 2
(i.e., on the back side of the insulating layer 7), and covers
substantially the entire back side 2B. The ground conductor plate 11 is
electrically connected to the ground conductor plate 8 by a plurality of
via-holes 13.

[0043] The via-holes 13 are each formed as a columnar conductor by
providing a through-hole penetrating the insulating layers 6 and 7 and
having an inside diameter of about several ten to several hundred lam
(e.g., 100 μm) and filling the through-hole with, for example, a
conductive metallic material such as copper or silver. The via-holes 13
extend in the Z-axis direction, and are connected to the ground conductor
plates 8, 11 at either end. The via-holes 13 are placed so as to surround
the strip conductor 12. Thus, the via-holes 13 serve to stabilize the
potential of the ground conductor plates 8, 11, and suppress leakage of
the high frequency signal that propagates through the strip conductor 12.

[0044] The strip conductor 12 can be made of, for example, a conductive
metallic material similar to that of the ground conductor plate 8. The
strip conductor 12 is formed in the shape of a narrow strip extending in
the X-axis direction. The strip conductor 12 is placed between the
insulating layer 6 and the insulating layer 7. An end of the strip
conductor 12 is placed in the center portion of the connecting aperture
8A, and is connected to the radiating conductor element 9 via the
via-hole 14 serving as a connecting line.

[0045] The via-hole 14 is formed as a columnar conductor in substantially
the same manner as the via-holes 13. The via-hole 14 penetrates the
insulating layers 5 and 6, and extends in the Z-axis direction through
the center portion of the connecting aperture 8A. The ends of the
via-hole 14 are respectively connected to the radiating conductor element
9 and the strip conductor 12. The strip line 10 is formed in line
symmetry with respect to a line passing through the center position in
the width direction and parallel to the X-axis.

[0046] The parasitic conductor element 15 is formed in a substantially
rectangular shape by using a conductive metallic material similar to that
of the ground conductor plate 8, for example. The parasitic conductor
element 15 is located on the side opposite to the ground conductor plate
8 as viewed from the radiating conductor element 9. The parasitic
conductor element 15 is placed on the front side 2A of the multilayer
substrate 2 (i.e., on the front side of the insulating layer 3). The
insulating layers 3 and 4 are placed between the parasitic conductor
element 15 and the radiating conductor element 9. Therefore, the
parasitic conductor element 15 faces the radiating conductor element 9 at
a distance while being insulated from the radiating conductor element 9
and the ground conductor plate 8.

[0047] As illustrated in FIG. 4, the parasitic conductor element 15 has a
width dimension L3 of, for example, about several hundred μm in the
Y-axis direction, and has a length dimension L4 of, for example, about
several hundred μm in the X-axis direction. The width dimension L3 of
the parasitic conductor element 15 is larger than the width dimension L1
of the radiating conductor element 9, for example. The length dimension
L4 of the parasitic conductor element 15 is smaller than the length
dimension L2 of the radiating conductor element 9, for example. The
relative sizes and specific shapes of the parasitic conductor element 15
and the radiating conductor element 9 are not limited to those mentioned
above but are set as appropriate by taking factors such as the radiation
pattern of the wideband patch antenna 1 into consideration. The parasitic
conductor element 15 produces electromagnetic coupling with the radiating
conductor element 9.

[0048] The coupling adjusting conductor plate 16 is formed in a
substantially rectangular shape by using a conductive metallic material
similar to that of the ground conductor plate 8, for example. The
coupling adjusting conductor plate 16 is placed between the radiating
conductor element 9 and the parasitic conductor element 15. Specifically,
as illustrated in FIGS. 2 and 3, the coupling adjusting conductor plate
16 is placed between the insulating layer 3 and the insulating layer 4,
and is insulated from the radiating conductor element 9 and the parasitic
conductor element 15.

[0049] As illustrated in FIG. 4, the coupling adjusting conductor plate 16
has a width dimension L5 of, for example, about several hundred μm in
the Y-axis direction, and has a length dimension L6 of, for example,
about several hundred μm in the X-axis direction. The width dimension
L5 of the coupling adjusting conductor plate 16 is, for example, larger
than the width dimension L1 of the radiating conductor element 9 and the
width dimension L3 of the parasitic conductor element 15. The length
dimension L6 of the coupling adjusting conductor plate 16 is, for
example, smaller than the length dimension L2 of the radiating conductor
element 9 and the length dimension L4 of the parasitic conductor element
15. Thus, the coupling adjusting conductor plate 16 crosses and covers a
center portion (for example, a center portion in the X-axis direction)
that is a part of the area where the radiating conductor element 9 and
the parasitic conductor element 15 overlap each other, in the Y-axis
direction. Therefore, the coupling adjusting conductor plate 16 straddles
the radiating conductor element 9 in a direction orthogonal to the
direction of the current I that flows in the radiating conductor element
9.

[0050] A pair of via-holes 17 are provided at both end sides of the
coupling adjusting conductor plate 16. The via-holes 17 are each formed
as a columnar conductor in substantially the same manner as the via-holes
13. The via-holes 17 penetrate the insulating layers 4 and 5, and
electrically connect the coupling adjusting conductor plate 16 and the
ground conductor plate 8 to each other.

[0051] The radiating conductor element 9, the parasitic conductor element
15, and the coupling adjusting conductor plate 16 can be provided in such
a way that, for example, their center positions are located at the same
position in the XY-plane. Also, the radiating conductor element 9, the
parasitic conductor element 15, and the coupling adjusting conductor
plate 16 can be formed in line symmetry with respect to a line passing
through their center positions and parallel to the X-axis, and can be
formed in line symmetry with respect to a line passing through their
center positions and parallel to the Y-axis. The coupling adjusting
conductor plate 16 adjusts the amount of coupling between the radiating
conductor element 9 and the parasitic conductor element 15.

[0052] The wideband patch antenna 1 according to this embodiment is
configured as mentioned above. Next, the operation of the wideband patch
antenna 1 is described.

[0053] First, when electric power is fed from the strip line 10 toward the
radiating conductor element 9, the current I flows in the radiating
conductor element 9 along the X-axis direction. Thus, the wideband patch
antenna 1 transmits or receives a high frequency signal according to the
length dimension L2 of the radiating conductor element 9.

[0054] At this time, the radiating conductor element 9 and the parasitic
conductor element 15 are electromagnetically coupled to each other and,
as illustrated in FIGS. 5 and 6, have two resonant modes with different
resonant frequencies. The return loss of high frequency signals decreases
at these two resonant frequencies. In addition, the return loss of high
frequency signals decreases also in the frequency range between these two
resonant frequencies. Therefore, the usable frequency range for high
frequency signals increases as compared with a case where the parasitic
conductor element 15 is omitted.

[0055] As the distance dimension between the parasitic conductor element
15 and the radiating conductor element 9 becomes larger, the frequency
range over which the strip line 10 and the radiating conductor element 9
are matched tends to increase. However, as the distance dimension between
the parasitic conductor element 15 and the radiating conductor element 9
becomes larger, the overall size of the resulting antenna increases,
which makes application of such an antenna to miniature electronic
devices difficult.

[0056] In contrast, according to this embodiment, the coupling adjusting
conductor plate 16 is provided between the radiating conductor element 9
and the parasitic conductor element 15. Therefore, the amount of coupling
between the radiating conductor element 9 and the parasitic conductor
element 15 can be adjusted by using the coupling adjusting conductor
plate 16.

[0057] To investigate the effect of the coupling adjusting conductor plate
16, the frequency characteristics of return loss were measured for a case
where the coupling adjusting conductor plate 16 is provided as in the
first (1st) embodiment, and a first comparative (1st comp.) example case
where the coupling adjusting conductor plate 16 is omitted. The results
are illustrated in FIG. 7. The thickness dimension of the multilayer
substrate 2 was set to 0.7 mm. The width dimension L1 of the radiating
conductor element 9 was set to 0.55 mm, and its length dimension L2 was
set to 0.7 mm. The width dimension L3 of the parasitic conductor element
15 was set to 1.15 mm, and its length dimension L4 was set to 0.6 mm. The
width dimension L5 of the coupling adjusting conductor plate 16 was set
to 1.5 mm, and its length dimension L6 was set to 0.3 mm. The diameter of
the via-holes 13, 14, and 17 was set to 0.1 mm.

[0058] The results in FIG. 7 show that in the case where the coupling
adjusting conductor plate 16 is not provided, i.e., as shown by the curve
labeled "1ST COMP. EXAMPLE (WITHOUT COUPLING ADJ. CONDUCTOR PLATE)," the
frequency bandwidth over which the return loss is below -8 dB is about 14
GHz. In contrast, in the case where the coupling adjusting conductor
plate 16 is provided i.e., as shown by the curve labeled "1ST EMBODIMENT
(WITH COUPLING ADJ. CONDUCTOR PLATE)," the frequency bandwidth over which
the return loss is below -8 dB is about 19 GHz, indicating an increase in
the corresponding bandwidth.

[0059] In this way, the coupling adjusting conductor plate 16 can adjust
the resonant frequency of current in accordance with its width dimension
L5, and can adjust the strength of electromagnetic coupling between the
radiating conductor element 9 and the parasitic conductor element 15 in
accordance with its length dimension L6.

[0060] An optimum value exists for the length dimension L6 of the coupling
adjusting conductor plate 16. For example, as illustrated as a second
comparative (2ND COMP.) example in FIG. 8, setting a small value (L6=0.2
mm) as the length dimension of the coupling adjusting conductor plate 16
can sometimes lead to smaller return loss on the high frequency side and
hence narrower bandwidth. On the other hand, as illustrated as a third
comparative (3RD COMP.) example in FIG. 8, setting an excessively large
value (L6=0.6 mm) as the length dimension of the coupling adjusting
conductor plate 16 can sometimes cause the return loss to rise in the
frequency range between the two resonant frequencies, resulting in
narrower bandwidth. For this reason, the length dimension L6 of the
coupling adjusting conductor plate 16 is preferably set to, for example,
about half the value of the length dimension L2 of the radiating
conductor element 9.

[0061] In this way, according to this embodiment, the coupling adjusting
conductor plate 16 partially covers, or overlaps the area where the
radiating conductor element 9 and the parasitic conductor element 15
overlap each other, and straddles the radiating conductor element 9 in a
direction orthogonal to the direction of the current I that flows in the
radiating conductor element 9. Therefore, when the radiating conductor
element 9 and the parasitic conductor element 15 are electromagnetically
coupled to each other, the strength of the electromagnetic coupling can
be adjusted by using the coupling adjusting conductor plate 16, thereby
increasing the frequency range over which matching is obtained between
the strip line 10 and the radiating conductor element 9.

[0062] Since the ground conductor plate 8 and the coupling adjusting
conductor plate 16 are provided to the multilayer substrate 2, the both
end sides of the coupling adjusting conductor plate 16 can be easily
connected to the ground conductor plate 8 by using the via-holes 17 that
penetrate the insulating layers 4 and 5 of the multilayer substrate 2.
Therefore, the potential of the coupling adjusting conductor plate 16 can
be stabilized, and also the electrical characteristics of the coupling
adjusting conductor plate 16 can be made symmetrical with respect to the
Y-axis direction, thereby suppressing occurrence of stray capacitance,
unwanted resonance phenomenon, and so on as compared with a case where
only one end side of the coupling adjusting conductor plate 16 is
connected to the ground conductor plate 8.

[0063] The ground conductor plate 8, the radiating conductor element 9,
the parasitic conductor element 15, and the coupling adjusting conductor
plate 16 are provided to the multilayer substrate 2 having the plurality
of laminated insulating layers 3 to 7. Therefore, by providing the
parasitic conductor element 15, the coupling adjusting conductor plate
16, the radiating conductor element 9, and the ground conductor plate 8
in order on the front sides of the different insulating layers 3 to 7,
respectively, these components can be easily placed at different
positions with respect to the thickness direction of the multilayer
substrate 2.

[0064] Further, the strip line 10 is located on the side opposite to the
radiating conductor element 9 as viewed from the ground conductor plate
8. Therefore, the strip line 10 can be formed together with the ground
conductor plate 8, the radiating conductor element 9, the parasitic
conductor element 15, and the coupling adjusting conductor plate 16, in
the multilayer substrate 2 provided with these components, thereby
improving productivity and reducing variations in characteristics.

[0065] Next, FIGS. 9 to 12 illustrate a second exemplary embodiment. The
characteristic feature of this embodiment resides in that a microstrip
line is connected to the radiating conductor element. In this embodiment,
components that are identical to those of the first exemplary embodiment
mentioned above are denoted by the identical symbols and are described
above.

[0066] A wideband patch antenna 21 according to the second exemplary
embodiment includes a multilayer substrate 22, the ground conductor plate
8, the radiating conductor element 9, the parasitic conductor element 15,
the coupling adjusting conductor plate 16, and the like. In substantially
the same manner as the multilayer substrate 2 according to the first
exemplary embodiment, the multilayer substrate 22 can be formed by an
LTCC multilayer substrate, for example, and has four insulating layers 23
to 26 that are laminated in the Z-axis direction from its front side 22A
toward its back side 22B.

[0067] In this case, the ground conductor plate 8 is provided between the
insulating layer 25 and the insulating layer 26, and covers substantially
the entire surface of the multilayer substrate 22. That is, the ground
conductor plate 8 covers substantially the entire upper surface of
insulating layer 26. The radiating conductor element 9 is located between
the insulating layer 24 and the insulating layer 25, and faces the ground
conductor plate 8 at a distance. The parasitic conductor element 15 is
provided on the front side 22A of the multilayer substrate 22 (i.e., on
the front side of the insulating layer 23). The parasitic conductor
element 15 is located on the side opposite to the ground conductor plate
8 as viewed from the radiating conductor element 9, and is insulated from
the radiating conductor element 9 and the ground conductor plate 8.

[0068] The coupling adjusting conductor plate 16 is provided between the
insulating layer 23 and the insulating layer 24, and is placed between
the radiating conductor element 9 and the parasitic conductor element 15.
The coupling adjusting conductor plate 16 partially covers (i.e.,
overlaps when viewed in the thickness direction) the area where the
radiating conductor element 9 and the parasitic conductor element 15
overlap each other, and straddles the radiating conductor element 9 in
the Y-axis direction. The both end sides of the coupling adjusting
conductor plate 16 are electrically connected to the ground conductor
plate 8 via the via-holes 17.

[0069] As illustrated in FIGS. 9 to 11, a microstrip line 27 is provided
on the side opposite to the radiating conductor element 9 as viewed from
the ground conductor plate 8. The microstrip line 27 forms a feed line
for feeding electric power to the radiating conductor element 9.
Specifically, the microstrip line 27 includes a strip conductor 28 that
is provided on the side opposite to the radiating conductor element 9 as
viewed from the ground conductor plate 8. The strip conductor 28 can be
made of a conductive metallic material similar to that of the ground
conductor plate 8, for example, and is formed in the shape of a narrow
strip extending in the X-axis direction. The strip conductor 28 is
provided on the back side 22B of the multilayer substrate 22 (the back
side of the insulating layer 26). The microstrip line 27 is formed in
line symmetry with respect to a line passing through the center position
in the width direction and parallel to the X-axis.

[0070] An end of the strip conductor 28 is placed in the center portion of
the connecting aperture 8A, and is connected to the radiating conductor
element 9 via a via-hole 29 serving as a connecting line. The via-hole 29
is formed in substantially the same manner as the via-hole 14 according
to the first exemplary embodiment. The via-hole 29 penetrates the
insulating layers 25 and 26, and extends in the Z-axis direction through
the center portion of the connecting aperture 8A. The ends of the
via-hole 29 are respectively connected to the radiating conductor element
9 and the strip conductor 28.

[0071] In this way, in this embodiment as well, an operational effect
similar to that of the first exemplary embodiment can be obtained. In
particular, in this embodiment, the microstrip line 27 is connected to
the radiating conductor element 9. Therefore, as compared with the strip
line 10 according to the first exemplary embodiment, the configuration of
the microstrip line 27 can be simplified, thereby reducing manufacturing
cost.

[0072] Next, FIGS. 13 and 14 illustrate a third exemplary embodiment. The
characteristic feature of this embodiment resides in that the coupling
adjusting conductor plate is connected to the ground conductor plate by
using via-holes that penetrate the multilayer substrate. In this
embodiment, components that are identical to those of the first exemplary
embodiment mentioned above are denoted by the identical symbols and are
described above.

[0073] A wideband patch antenna 31 according to the third exemplary
embodiment includes a multilayer substrate 32, the ground conductor plate
8, the radiating conductor element 9, the parasitic conductor element 15,
a coupling adjusting conductor plate 40, and the like. The multilayer
substrate 32 is formed in substantially the same manner as the multilayer
substrate 22 according to the second exemplary embodiment. The multilayer
substrate 32 has four insulating layers 33 to 36 that are laminated in
the Z-axis direction from its front side 32A toward its back side 32B.

[0074] In this case, the ground conductor plate 8 is provided between the
insulating layer 35 and the insulating layer 36, and covers substantially
the entire surface of the multilayer substrate 32. That is, the ground
conductor plate 8 covers substantially the entire upper surface of
insulating layer 36. The radiating conductor element 9 is located between
the insulating layer 34 and the insulating layer 35, and faces the ground
conductor plate 8 at a distance. The parasitic conductor element 15 is
provided on the front side 32A of the multilayer substrate 32 (i.e., on
the front side of the insulating layer 33). The parasitic conductor
element 15 is located on the side opposite to the ground conductor plate
8 as viewed from the radiating conductor element 9, and is insulated from
the radiating conductor element 9 and the ground conductor plate 8.

[0075] The microstrip line 37 is formed in substantially the same manner
as the microstrip line 27 according to the second exemplary embodiment.
The microstrip line 37 includes a strip conductor 38 that is provided on
the side opposite to the radiating conductor element 9 as viewed from the
ground conductor plate 8. The strip conductor 38 can be made of a
conductive metallic material similar to that of the ground conductor
plate 8, for example, and is formed in the shape of a narrow strip
extending in the X-axis direction. The strip conductor 38 is provided on
the back side 32B of the multilayer substrate 32 (i.e., on the back side
of the insulating layer 36).

[0076] An end of the strip conductor 38 is placed in the center portion of
the connecting aperture 8A, and is connected to the radiating conductor
element 9 via a via-hole 39 serving as a connecting line. The via-hole 39
is formed in substantially the same manner as the via-hole 14 according
to the first embodiment. The via-hole 39 penetrates the insulating layers
35 and 36, and extends in the Z-axis direction through the center portion
of the connecting aperture 8A. The ends of the via-hole 39 are
respectively connected to the radiating conductor element 9 and the strip
conductor 38.

[0077] The coupling adjusting conductor plate 40 can be formed in
substantially the same manner as the coupling adjusting conductor plate
16 according to the first exemplary embodiment. The coupling adjusting
conductor plate 40 is provided between the insulating layer 33 and the
insulating layer 34, and is placed between the radiating conductor
element 9 and the parasitic conductor element 15. The coupling adjusting
conductor plate 40 partially covers, or overlaps the area where the
radiating conductor element 9 and the parasitic conductor element 15
overlap each other, and straddles the radiating conductor element 9 in
the Y-axis direction.

[0078] However, the coupling adjusting conductor plate 40 differs from the
coupling adjusting conductor plate 16 according to the first exemplary
embodiment in that the both end sides of the coupling adjusting conductor
plate 40 are electrically connected to the ground conductor plate 8 by
using via-holes 41 that penetrate the multilayer substrate 32. In this
case, like the via-holes 17 according to the first exemplary embodiment,
the via-holes 41 each form a columnar conductor. The via-holes 41
penetrate all of the insulating layers 33 to 36 of the multilayer
substrate 32. Therefore, the via-holes 41 extend in the Z-axis direction,
and are connected at some point along the Z-axis direction to each of the
ground conductor plate 8 and the coupling adjusting conductor plate 16.

[0079] In this way, in this embodiment as well, an operational effect
similar to that of the first exemplary embodiment can be obtained. In
particular, in this embodiment, the coupling adjusting conductor plate 40
is connected to the ground conductor plate 8 by using the via-holes 41
that penetrate the multilayer substrate 32. Therefore, even in a case
where it is difficult to form via-holes that provide connection between
specific layers, the via-holes 41 formed by through via-holes can be
easily formed.

[0080] While the above description of the third exemplary embodiment is
directed to the case of an application to the wideband patch antenna 31
that includes the microstrip line 37 as in the second embodiment,
embodiments according to the present disclosure may be applied to a
wideband patch antenna that includes a strip line as in the first
exemplary embodiment mentioned above.

[0081] Next, FIGS. 15 and 16 illustrate a fourth exemplary embodiment. The
characteristic feature of this embodiment resides in that the parasitic
conductor element is formed by a substantially rectangular conductor
plate that is cut off at the corner portion. In this embodiment,
components that are identical to those of the first exemplary embodiment
mentioned above are denoted by the identical symbols and are described
above.

[0083] The parasitic conductor element 52 is formed in substantially the
same manner as the parasitic conductor element 15 according to the first
exemplary embodiment. However, the parasitic conductor element 52
according to this embodiment is formed by a substantially rectangular
conductor plate having a cut-off part 52A where the corner portion of the
parasitic conductor element 52 is cut off. While the cut-off part 52A of
the parasitic conductor 52 is cut off linearly in the present case, the
cut-off part 52A may be cut off in an arcuate shape, for example.

[0084] The path of the current flowing in the parasitic conductor element
52 varies with the shape of the cut-off part 52A. Therefore, the amount
of coupling between the radiating conductor element 9 and the parasitic
conductor element 52 can be adjusted by setting the shape of the cut-off
part 52A as appropriate.

[0085] To investigate the effect of the cut-off part 52A, the frequency
characteristics of return loss were measured for a case where the corner
portion is cut off according to the fourth embodiment (4TH EMBODIMENT),
and a fourth comparative example (4TH COMP. EXAMPLE) case where the
corner portion is not cut off. The results are illustrated in FIG. 17.

[0086] The results in FIG. 17 show that in the case where the corner
portion is not cut off, the return loss rises to about -8 dB in the
frequency range between the two resonant frequencies. In contrast, in the
case where the corner portion is cut off, as compared with the case where
the corner portion is not cut off, although the resonant frequency on the
low frequency side shifts to the high frequency side, the return loss
drops below -10 dB in the frequency range between the two resonant
frequencies. Therefore, the frequency bandwidth over which the return
loss drops below -10 dB is about 15 GHz, indicating an increase in the
corresponding bandwidth.

[0087] In this way, in this embodiment as well, an operational effect
similar to that of the first exemplary embodiment can be obtained. In
particular, in this embodiment, the parasitic conductor element 52 is
formed by a substantially rectangular conductor plate having the cut-off
part 52A where the corner portion of the parasitic conductor element 52
is cut off. Therefore, the amount of coupling between the parasitic
conductor element 52 and the radiating conductor element 9 can be
adjusted by adjusting the path of the current flowing in the parasitic
conductor element 52, thereby lowering return loss. Therefore, the
frequency range over which the strip line 10 and the radiating conductor
element 9 are matched can be increased, thereby achieving bandwidth
enhancement.

[0088] While the above description of the fourth exemplary embodiment is
directed to the case of an application to the wideband patch antenna 51
similar to that of the first exemplary embodiment, embodiments according
to the present disclosure may be applied to the wideband patch antenna
21, 31 according to the second or third exemplary embodiments.

[0089] While the above description of exemplary embodiments is directed to
the case of the wideband patch antenna 1, 21, 31, 51 formed on the
multilayer substrate 2, 22, 32, a wideband patch antenna may be formed by
providing a single-layer substrate with a conductor plate and the like.

[0090] While the above description of exemplary embodiments is directed to
the case of using the strip line 10 or the microstrip line 27, 37 as a
feed line, for example, other kinds of feed lines such as a coaxial cable
may be used.

[0091] While the above description of the embodiments is directed to the
case of a wideband patch antenna used for millimeter waves in the 60 GHz
band, embodiments according to the present disclosure may be applied to
wideband patch antennas used for millimeter waves in other frequency
ranges, microwaves, or the like.

[0092] According to embodiments of the present disclosure, the coupling
adjusting conductor plate partially covers (i.e., overlaps) the area
where the parasitic conductor element and the radiating conductor element
overlap each other, and straddles the radiating conductor element in a
direction orthogonal to the direction of the current that flows in the
radiating conductor element. Therefore, when the radiating conductor
element and the parasitic conductor element are electromagnetically
coupled to each other, the strength of the electromagnetic coupling can
be adjusted by using the coupling adjusting conductor plate, thereby
increasing the frequency range over which matching is obtained between
the feed line and the radiating conductor element.

[0093] Specifically, when the width direction of the coupling adjusting
conductor plate is made parallel to the direction of the current that
flows in the radiating conductor element, by adjusting the width
dimension of the coupling adjusting conductor plate, the strength of the
magnetic coupling between the radiating conductor element and the
parasitic conductor element can be adjusted. Also, when the length
direction of the coupling adjusting conductor plate is made orthogonal to
the direction of the current that flows in the radiating conductor
element, by adjusting the length dimension of the coupling adjusting
conductor plate, the resonant frequency of current can be adjusted.

[0094] For example, in a case where the ground conductor plate and the
coupling adjusting conductor plate are provided to a substrate made of an
insulating material, the ground conductor plate and the coupling
adjusting conductor plate can be easily connected to each other by using
via-holes provided in the substrate. Therefore, soldered connections can
be obviated to simplify assembly and increase productivity. Moreover,
variations in characteristics among individual antennas can be reduced.

[0095] According to embodiments in which both end sides of the coupling
adjusting conductor plate are connected to the ground conductor plate by
using a columnar conductor, in a case where the ground conductor plate
and the coupling adjusting conductor plate are provided to a substrate
made of an insulating material, the ground conductor plate and the
coupling adjusting conductor plate can be easily connected to each other
by using a via-hole forming a columnar conductor which is provided in the
substrate.

[0096] In embodiment in which the feed line includes a strip line, where
the strip line has another ground conductor plate that is provided on a
side opposite to the radiating conductor element as viewed from the
ground conductor plate, a strip conductor is provided between the other
ground conductor plate and the ground conductor plate, and the strip
conductor of the strip line connects to the radiating conductor element
via a connecting aperture that is provided in the ground conductor plate,
in a case where the ground conductor plate, the radiating conductor
element, and the coupling adjusting conductor plate are provided to a
substrate made of an insulating material, the strip line can be formed in
the substrate together with these components, thereby improving
productivity and reducing variations in characteristics.

[0097] In embodiments in which the feed line includes a microstrip line,
where the microstrip line has a strip conductor that is provided on a
side opposite to the radiating conductor element as viewed from the
ground conductor plate, and the strip conductor of the microstrip line
connects to the radiating conductor element via a connecting aperture
that is provided in the ground conductor plate, in a case where the
ground conductor plate, the radiating conductor element, and the coupling
adjusting conductor plate are provided to a substrate made of an
insulating material, the microstrip line can be formed in the substrate
together with these components, thereby improving productivity and
reducing variations in characteristics.

[0098] In embodiments in which the parasitic conductor element includes a
substantially rectangular conductor plate that is cut off at a corner
portion, by adjusting the path of the current flowing in the parasitic
conductor element, the amount of coupling between the parasitic conductor
element and the radiating conductor element can be adjusted, thereby
increasing the frequency range over which the feed line and the radiating
conductor element are matched.

[0099] In embodiments in which the ground conductor plate, the radiating
conductor element, the parasitic conductor element, and the coupling
adjusting conductor plate are provided to a multilayer substrate having a
plurality of laminated insulating layers, and are placed at positions
different from each other with respect to a thickness direction of the
multilayer substrate, by providing the ground conductor plate, the
radiating conductor element, the parasitic conductor element, and the
coupling adjusting conductor plate on the front sides of different
insulating layers, these components can be easily placed at different
positions with respect to the thickness direction of the multilayer
substrate. As a result, productivity can be increased, and variations in
characteristics among individual antennas can be reduced.